Hi! On 2022-03-22T14:41:46+0100, Tom de Vries via Gcc-patches <gcc-patches@gcc.gnu.org> wrote: > Starting with ptx isa version 6.3, a ptx directive .alias is available. > Use this directive to support symbol aliases, as far as possible.
> The alias support has the following [and more] limitations. > Aliases to aliases are not supported (see libgomp.c-c++-common/pr96390.c). > This is currently not prohibited by the compiler, but with the driver link we > run into: "Internal error: alias to unknown symbol" . Prathamesh in <https://inbox.sourceware.org/ia1pr12mb903193cdae8c74b8c44b4621ce...@ia1pr12mb9031.namprd12.prod.outlook.com> "[nvptx] Fix code-gen for alias attribute" has proposed a way to make these work, to a degree, via resolving to 'ultimate_alias_target'. > Unreferenced aliases are not emitted (these can occur f.i. when inlining a > call to an alias). This avoids driver link error "Internal error: reference > to deleted section". That is, indeed, (still) necessary, but also problematic: if the reference (use) of the alias is in a different compilation unit ("there"), we can't detect that "here" when deciding to not emit the alias that's unused "here", and we then run into an unresolved symbol "there". (I've not yet spent further thoughts on this, in the current GCC/nvptx using PTX '.alias' scenario.) > At some point we may add support in the nvptx-tools linker for symbol > aliases, and define f.i. malias=ptx and malias=ld to choose between the two in > the compiler. I'm working on that: <https://gcc.gnu.org/PR105018> "[nvptx] Need better alias support", via <https://github.com/SourceryTools/nvptx-tools/issues/32> "[LD] Handle alias in nvptx-ld as nvptx's .alias does not handle it fully". > [nvptx] Use .alias directive for mptx >= 6.3 > --- a/gcc/config/nvptx/nvptx.cc > +++ b/gcc/config/nvptx/nvptx.cc > @@ -968,7 +969,8 @@ static void > write_fn_proto_1 (std::stringstream &s, bool is_defn, > const char *name, const_tree decl) > { > - write_fn_marker (s, is_defn, TREE_PUBLIC (decl), name); > + if (lookup_attribute ("alias", DECL_ATTRIBUTES (decl)) == NULL) > + write_fn_marker (s, is_defn, TREE_PUBLIC (decl), name); This non-emitting of DECL and DEF linker markers for aliases is problematic, as I'll discuss in the following. Grüße Thomas
